gfx: changed minimum-supported OpenGL version to 3.3.¹

1: OpenGL 2.1 is too crippling in mock-design. Also, a ton of
hardware supports 3.3,² so we get to have our cake and even eat
the bits that GLaDOS didn't burn...

2: Ref: Steam Dev Days 2014: Moving Your Games to OpenGL.
http://youtu.be/45O7WTc6k2Y
http://media.steampowered.com/apps/steamdevdays/slides/movingtoopengl.pdf
array: removed <utility> include; tidy.
fixed_array: new collection class.
test/collections/fixed_array: new test. Updated test/general/headers.